Sulfur-containing polythioether prepolymers are known to be useful in aerospace sealant applications. Polythioether prepolymers can be prepared by reacting a polythiol with a divinyl ether to provide prepolymers that provide sealants that meet the demanding performance requirements of the aerospace industry.
Among other requirements, aerospace sealants must be resistant to aerospace fluids including aviation fuel. Fuel resistance can be imparted to a sealant by including sulfur atoms in the backbone of the prepolymer. Divinyl ethers used to prepared polythioethers have not included sulfur atoms.
For certain aerospace sealant uses it can be desirable that the sealant cure rapidly following application to a surface.
For certain aerospace sealants it can also be desirable that the sealant contain a high loading of filler. Filler can be included in a sealant for a number of reasons such as to improve the physical properties of the cured sealant, to reduce the weight, to impart electrical conductivity, and/or to impart RFI/EMI shielding effectiveness. The addition of filler can increase the viscosity of the sealant, which can make the sealant difficult to apply. It can be desirable to reduce the viscosity of sealants containing fillers and especially those having a high filler content. Viscosity of compositions containing fillers can be reduced using plasticizers such as reactive diluents and lower molecular weight reactants. However, the addition of these additives can compromise the properties of the cured sealant.
Therefore, it is desirable to provide polythioether prepolymers that cure rapidly, exhibit improved fuel resistance, and for sealants having a high loading of filler particles, filler compatibility.